I can't think of any other way to describe what is going on. At highway speeds, the truck will act like it is jumping out of gear them slams back. I can't see any change RPM change on the tach as it happens quickly, I drive 50 miles round trip to work, some days it doesn't do it all, other times it might do it once, or several times, sometimes several times in a matter of minutes. There is no pattern as to when it occurs, I have felt it a few times at lower speeds, 35-mph, but most of the time it is 60-85. The transmission has about 50k on it since overhaul.
Thoughts ? I know it is a pain to find something that you cannot get to fail in front of you.

 

Could be throttle position sensor, or a bad connection somewhere, or a bad solenoid in the trans.